1. Field of the Invention
The present invention relates to an amplifier, and more specifically to a trans-impedance amplifier that converts a current signal into a voltage signal with amplification.
2. Description of the Related Art
An optical receiver used in an optical communication system often includes a differential amplifier that amplifies a differential input signal. The Patent Literatures 1 to 3 have disclosed some configurations of the differential amplifier.
The Patent Literature 1 has disclosed a configuration that comprises a differential amplifier and an offset compensator. The differential amplifier amplifies an input signal input through a coupling capacitor and outputs the amplified signal as a differential output signal. The offset compensator includes a low pass filter that passes and outputs only low frequency components less than a cutoff frequency of the differential output signal and a bias adjusting circuit that adjusts a DC bias potential of the differential input signal depending on the low frequency components output from the low pass filter.
The Patent Literature 2 has disclosed a configuration that includes a trans-impedance differential amplifier and a bypass circuit. The trans-impedance differential amplifier converts an input current signal into an output voltage signal with amplification. The bypass circuit bypasses an excessive portion of the input current signal as a bypass current so as to prevent the output voltage signal from being saturated and maintain gain of the amplification less than a predetermined value for avoiding oscillation against an input current signal with large magnitude.
The Patent Literature 3 has disclosed a configuration that includes a differential amplifier, a threshold circuit, and a filter circuit. The differential amplifier has a pair of input terminals. The one of the input terminals receives a photocurrent output from a photodetector (PD) and the other of the input terminals receives a threshold supplied from the threshold circuit. The filter circuit is connected between the differential amplifier and the threshold circuit, and includes a multiple filter attributed to at least two time constants.    Patent Literature 1: Japanese Patent Application Laid-Open No. H7-240640.    Patent Literature 2: Japanese Patent Application Laid-Open No. 2000-349571.    Patent Literature 3: Japanese Patent Application Laid-Open No. 2010-136169.